Electrical capacitor having a silicon nitride dielectric



June 25,1963 c. R. BARNES ETAL 3,095,527

ELECTRICAL CAPACITOR HAVING A smcou NITRIDE DIELECTRIC Original FiledAug. 31, 1959 2 Sheets-Sheet 1 a: go; #3 n: T 8B; "1

w 8 mm @IN E Ego: +1 8 i- (L2 U Q o co m INVENTORS CHARLES R. BARNESCHARLES R. GEESNER 'x ATTo'RNdS June 25, 1963 c. R. BARNES ETAL3,095,527

ELECTRICAL CAPACITOR HAVING A SILICON NITRIDE DIELECTRIC Original FiledAug. 31, 1959 2 Sheets$heet 2 INDUCTION HEATER TEMPERATURE 3s CONTROLINVENTORS F -'1 ,2 CHARLES R. BARNES El CHARLES R. EESNER ATTO R NEYSUnited States Patent i 3,095,527 ELECTRICAL CAPACITOR HAVING A SILICONNITRIDE DIELECTRIC Charles R. Barnes, Medway, and Charles R. Geesner,Waynesville, Ohio, assignors to the United States of America asrepresented by the Secretary of the Air Force Original application Aug.31, 1959, Ser. No. 837,306, now Patent No. 3,038,243, dated June 12,1962. Divided and this application Dec. 5, 1960, Ser. No. 73,939

6 Claims. (Cl. 317-258) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the United States Government for governmental purposes withoutpayment to us of any royalty there-on.

This invention pertains to a capacitor and more particularly to acapacitor that is operatively stable at 600 C.

The invention disclosed herein is restricted from the aplication SerialNo. 837,306, filed August 31, 1959, now Patent No. 3,038,243, forSilicon Nitride Dielectric, that describes and claims the method bywhich the capacitor that is disclosed herein is made.

At the present time there is an increasing requirement in the militaryfield for dielectric materials such as are employed in capacitors andthe like to withstand environmental temperatures of the order of 500 C.and above. Ceramic and dielectric materials while capable ofwithstanding high temperatures unfortunately suffer a great increase inthe dissipation factor at temperatures of the order of 500 C. Thisinvention pertains to an improved dielectric material comprising thenonporous film of silicon nitride deposited on a metal substrate andforming the dielectric material in a capacitor or the like. The siliconnitride can also be employed as an encapsulating material to protectcapacitor assemblies in accordance with the invention from oxidation :attemperatures of 500 C. The invention relates to capacitors which employsilicon nitride as a dielectric in the form of nonporous silicon nitridefilms or coatings.

Briefly, a capacitor made in accordance with the invention, comprises athin metal disc or wafer substrate that has deposited on one sidethereof a coating of silicon nitride dielectric and a second capacitorplate deposited over the dielectric in the form of a thin conductingmetal film. The capacitor leads are soldered to the metal substrate andto the conductive coating on the dielectric material. In order toprevent oxidation or the capacitor plates the capacitor may becompletely i-nclosed within a silicon nitride encapsulation.

The capacitor in accordance with the invention is unique in that itselectrical characteristics are satisfactory in high temperatureenvironments as as 600 C. The method of making a capacitor in accordancewith the invention comprises placing a clean substrate disc ofmolybdenum or other suitable metal on a graphite core in a closeddeposition chamber with the core surrounded 'by a heating coil suppliedwith radio frequency current to heat the core by induction or eddycurrent heating to thereby heat the substrate. The heating current iscontrolled thermostatically with the substrate at surface temperature of960 C12. While the substrate is at the controlled temperature, a mixtureof clean and dry hydrogen and nitrogen gases and silicon bromide vaporis directed onto the surface of the substrate, chemical action causesthe silicon bromide to decompose and the silicon to unite Withthenitrogen to be deposited as a strongly adherent film of Si N (siliconnit-Bide) on w e surface of the substrate. SiBr H N are exhausted tohood.

The metal substrate disc is then removed from the Patented June 25, 1963deposition chamber and transferred to other apparatus including adeposition chamber in which a metal film is deposited on the substrateto form the second plate of the capacitor. In the case of gold, the goldmay be plated by the well known vacuum evaporation process in which goldis evaporated in an evacuated chamber and plated from the vapor phase onthe silicon nitride coating on the substrate. *In other cases platingmay be accomplished by chemical decomposition of metal chlorides orcarbonyl chlorides in a manner hereinafter as completely described.

The capacitor thus formed may have gold or platinum wires suitablysoldered by the use of gold or gold alloy or other high temperaturesolder to the plates of the condenser.

Where required the condenser assembly may be transferred to the originalapparatus and completely coated on all sides with a thin film oi?silicon nitride so as to encapsulate the condenser assembly to preventoxidation of the capacitor plates. More complete details of theinvention in all its aspects will become more apparent by reference tothe detailed description hereinafter given taken in conjunction with thedisclosure in which:

FIG. 1 is an apparatus diagram used in the description of theapplication of silicon nitride to a molybdenum substrate disc in theproduction ot a capacitor that embodies the present invention;

FIG. 2 is an apparatus diagram used in the description of theapplication of molybdenum on top of the silicon nitride coat applied tothe molybdenum substrate disc by the use of the equipment in FIG. 1;

FIG. 3 is an enlarged perspective view of "an inductively heated coreused as a part of the furnace in both FIGS. 1 and 2;

FIG. 4 is an enlarged sectional view taken across a diameter of thecapacitor that is produced by the use of the equipment in FIGS. 1 to 3,inclusive, and using the process that is disclosed herein as a part ofthe invention; and

FIG. 5 is a diminished plan view of the capacitor shown in section inFIG. 4.

The apparatus that is shown in FIG. 1 of the accompanying drawingsconsists of a bottle 1 of hydrogen gas and a bottle 2 of nitrogen gasthat are released from the bottles by valves 3 and 4 at rates determinedby flowmeters 5 and 6, respectively throughout. Illustrative gas flowrates are H 300 cos. per minute, and N 1100 cos. per minute.Illustrative fiowm'eters are glass tubes with upwardly expanding taperedbores containing observable floats 7 and 8. The floats 7 and 8 aredisplaced upward- -1y against gravity by the gas flow within the bore ofincreasing diameter along rate flow indicating scales, therebyindicating the rate of gas flow from the tanks 1 and 2, respectivelythroughout.

The hydrogen gas from the tank 1 is deoiridized in a deoxidizer 9 thatcatalvtically removes any oxygen present. The H gas illustratively ispassed over the catalyst palladium on a dehydrated oxide taken from thegroup of oxides of aluminum and zirconium. The nitrogen gas from thetank 2 is passed through copper turnings 10 Within a heated quartz tube11. The two gases are then joined in a common gas conductor at the valve12. A temperature controller 13 maintains the energization of anoutwardly insulated Nichrome winding 14 around the quartz tube 11 at apredetermined value of 700 C. to 800 C. The copper :turnings at thistemperature combine with any oxygen in the nitrogen gas.

A water drainage valve 15 at a vapor discharge end of the tube 11permits the drainage of water from the line after each plating run inreducing the copper oxide with hydrogen in the reactivation of thecopper turnings. The

water vapor produced is exhausted through the valve 15 to theatmosphere. Following the reduction of the copper the valve 15 is closedand the valve 12 is opened. The drying towers 16, 17 and 18illustratively may contain calcium hydride of particle size range ofpreferably from 4 to +40 mesh per inch.

The line valve 25 controls the flow of gas past the silicon tetrabromideassembly. The gas flow is bypassed through the bottle 20 by the openingof the bypass valves 26, 27, and 28 and the partial closing of the linevalve 25.

The bottle 20 contains silicon tetrabromide 21 in the liquid state. Themixed H and N carrier gas that enters the bottle 20 passes over thesurface of the silicon tetrabromide and picks up its vapor.

The bypassed gas is measured by a iiowmete-r 22 wherein a float 23 in atapered bore is supported against the pull of gravity. An illustrativeflow rate of the bypassed gas is 100 cos. per minute.

The silicon tetrabromide laden gas passes from the bottle 20 through thevalve 23 and back into the gas line to the deposition chamber 29. Thegas line between the silicon tetrabromide bypass and the depositionchamber 29 may be joined by a rubber tube 19 that is preferred for theconvenient interchange of deposition chamber equipment.

The deposition chamber 29 is closed at its upper end by a stopper 30through which extends a gas and vapor feed pipe 31 and is closed at itslower end by a stopper 66. The pipe 31 extends axially of the depositionchamber 29 and terminates downwardly in a nozzle 32 that is spaced atillustratively 4% inches above a molybdenum disc 33 that serves as asubstrate in the making of the capacitor in accordance with theinvention.

Within the deposition chamber 29 the substrate 33 rests on top of acylindrical core 34 of graphite or the like. A copper tubing watercooledcoil 35 surrounds the graphite core 34 and heats the core by induction.Radio frequency induction heater 36 supplies electrical power to thecoil 35 through the pair of leads 37. Both the coil 35 and the leads 37are watercooled.

The deposition chamber temperature of the substrate 33 is maintained ata prescribed value by means of a thermocouple 38 contacting the core 34which passes its output over the pair of leads 39 to a well known typeof adjustable automatic temperature controller 40.

The temperature controller 40 is operatively connected to the radiofrequency induction heater 36 so as to control the magnitude of theplate voltage supplied to the radio frequency oscillator and to thuscontrol the oscillator output to regulate the temperature.

Gases introduced into the deposition chamber 29 through the pipe 31 passfrom the deposition chamber to an exhaust stack 41 for their dischargeinto the atmos phere.

The product from the use of the equipment shown in FIG. 1 is amolybdenum disc 33 with a coat of silicon nitride 43 on one facethereof, as indicated in FIG. 4.

An illustrative Mo substrate disc is 0.005 inch in thickness and 1 inchin diameter. At the start of the making of a capacitor the Mo disc 33illustratively is cleaned in succession with acetone, a hot Watersolution of NaOH, hot chromic acid, distilled Water and finally the discis placed in the deposition chamber and is reduced with hydrogen atabout 600 C.

The first stage product is made by placing a clean substrate molybdenumdisc 33 on top of the graphite core 34 and setting the temperaturecontrol 40 for maintaining the surface of the disc at a temperaturewithin the range of from 930 C. to 1030 C. This temperature rangepermits the pyrolytic deposition of silicon nitride on the upper surfaceof the substrate. The preferred temperature range for the deposition ofoptimum quality films of silicon nitride on the molybdenum discs is 960C.- -l.

The thickness of the deposition of silicon nitride 43 on the Mo discmaintained at this temperature and with a gas V winding 56 that extendsaround the tube.

4 flow rate of 100 ccs. per minute as indicated by the meter 22, isabout one-half mil thickness of silicon nitride per hour. This thicknessis adequate for capacitor use.

The second stage in the production of the capacitor in accordance withinvention is by the use of the apparatus that is illustrated in FIG. 2of the drawings. The components in FIG. 2 that correspond in structureand function to those in FIG. 1 bear corresponding reference numeralsprimed in FIG. 2.

The apparatus in FIG. 2 comprises a source of hydrogen gas, such as theH tank 1 from which the gas flow is regulated by operation of the valve3' as indicated by the position of the float 7 along the flow rateindicating scale of the flowmeter 5.

Hydrogen gas from the pressurized tank 1 passes through the fiowmeter'5' and then any oxygen with it is removed by the deoxidizer 9". Thedeoxidized gas passes to at least one drying tower 16' that is filledwith calcium hydride for the purpose of removing traces of moisture fromthe hydrogen. The ground glass couplings 19 and 19" permit theinterchange in the top of the deposition chamber 29 and 29' of thestopper 30 carrying the pipe 31 in FIG. 1 with the stopper 45 carryingthe brass tube 46 and the Pyrex molybdenum pentachloride evaporator 48in FIG. 2. A variac or adjustable resistance 47 is removably connectedto the brass tube 46.

The variac 47 is provided with two covered wires 49 and 50. The variacwire 49 is connected by solder 51 to the brass tube 46. The other variacwire 56 is threaded from the top down through the brass tube 46 prior tothe insertion of the upper end of the brass tube into the lower end ofthe rubber tube 19. The lower end of the brass tube 46 in the stopper 53supports the M001 evaporator 48 within the deposition chamber 29'. Thelower end of I the wire passes between the stopper 53 and the tube mouthof the Pyrex evaporator 48. The wire 50 is connected at a glass anchor55 to a tube heating Nichrome The opposite end of the winding 56 isanchored mechanically at a second tube glass anchor 57 from which itcontinues to its electrical connection at the soldered union 58 with thelower end of the brass tube 46.

The Pyrex molybdenum pentachl-oride evaporator 48 is charged with MoClThe evaporator 48 has a side arm 59 that opens into the interior of theevaporator well above the top of the MoCl and discharges H carrying MoClvapor downwardly against the silicon nitride coat 43 on the molybdenumsubstrate 33' resting on the top of the deposition chamber graphite core34. Exhaust stack 41' exhausts gas and excess vapor from the depositionchamber 29'.

In the operation of the equipment that is illustrated in FIG. 2, thesubstrate 33', that has one silicon nitride coat 43, shown in FIG. 4,adhered to one side of the substrate by the use of the equipment in FIG.1, remains on the upper surface of the deposition chamber graphite core34'. The deposition chamber stopper 30 and the tube 31 are removed fromthe deposition chamber 29 and are replaced by the stopper 45 withits'connected variac 47 and molybdenum pentachloride evaporator 48. i

The next step in the production .of the capacitor that is contemplatedhereby as applied to FIG. 2 is the adjusting of the valve 3' for theflow of hydrogen from the tank 1' at .a preferred rate such as one literper minute to purge cut the equipment. The variac 47 is adjusted tomaintain the evaporator 48 at a preferred temperature of 194 C. Thedeposition chamber temperature control 40 is adjusted to a preferredsubstrate surface temperature of 810 C. When the system has arrived atan equilibrium operating condition the hydrogen valve 3 is maintained ata flow rate :of one liter of hydrogen per minute.

The hydrogen gas then serves as a carrier gas in entering the molybdenumpentachloride evaporator 48, picking up molybdenum chloride vapor anddischarging the gas mixture directly against the silicon nitride 43,which is on substrate 33 at the surface temperature of 810 C. asmeasured by an optical pyrometer. The gas exhaust stack 41' relieves thepressure above ambient from inside the deposition chamber 29'. At thistemperature molybdenum metal 44 is deposited on the surface of thesilicon nitride 43, as indicated in the sectional view in FIG. 4. Theplates 33 and 44 on opposite sides of the dielectric 43 then provides acapacitor.

A satisfactory useful capacitor comprises a molybdenum disc one inch indiameter and 10- inch thick. It bears a silicon nitride fil-m 43 that is5 X" inch thick and a molybdenum film 44 that is 5 'l0- inch thick.Under the described conditions and a H gas flow rate of one liter perminute and using the described equipment, the deposition of the Mo film5 X 10- inch thick requires about five minutes time.

The shorting of the capacitor plates 33 and 44 which occurs during thedeposition of the Mo film is removed by clamping a rubber stopper on topof the Mo film and etching back the thin Mo film 44 with dilute nitricacid for about ,4 inch from the outer circumference of the capacitorradially to the edge of the stopper, to provide the capacitor structureindicated in section in FIG. 4.

Electrical lead attachment areas are then provided as indicated in FIGS.4 and 5 of the drawings, by dissolving away a small spot of the thin Mofilm with a drop of nitric acid. Beneath this first spot scratch away asmaller spot of Si N film 43 over a suflicient area on the substrate 33to attach an end of a first lead 60 to the substrate. The coatedsubstrate is then returned to the deposition chamber. Platinum leads 60and 61 then are each supported by a suitable length of glass tubing, notshown, a tapered end of which is imbedded in the stopper 66. The upperend of these glass tubes then will support the leads by inserting theleads in the open upper ends of the glass tubes. The unsupported ends ofthe leads are bent over to rest against the bare spot on the substrateand on the molybdenum film respectively. A bead of gold is placedadjacent to the tip of each wire. The stopper 30 and its pipe 31 arereplaced to close the deposition chamber. The temperature control isadjusted to cause the gold to flux and form beads 62 and 63 at the tipsof the wires 60 and 61 against the substrate 33 and the Mo layer 44,respectively throughout. This completes the construction of thecapacitor which embodies this invention in its unencapsulated form.

The encapsulation of the capacitor is started by adjusting thetemperature of the capacitor in the deposition chamber to within therange of from 960 to 1030 C. The capacitor with its leads 60 and 61attached to the two capacitor plates is encapsulated with-in a skin coat64 of Si N using the equipment in FIG. 1 and the described process; Theencapsulating Si N is deposited to a desired thickness preferably onboth sides of the capacitor. The capacitor is structurally andfunctionally complete for its use and operation up to about 600 C. Thecapacitor plates are protected fro-m'oxidation damage up to about 1000C. when encapsulated with silicon nitride.

Commercial grades of hydrogen and nitrogen may be used with adequatepurification facilities. The quartz tube 11 containing copper turnings10 preferably is maintained at from 700 to 800 C. to form copper oxideof any oxygen in the gas passed through the tube. The copper turnings 10are reactivated after each plating run by flushing hydrogen gasbackwards through the quartz tube 11 and over the copper turnings 10,thereby removing the oxygen from the copper oxide as water vapor whichis exhausted to the atmosphere by opening the valve 15, closing thevalve 12 and using hydrogen from the tank -1. The valve 4 is openedsufliciently to provide a suificient flow of nitrogen to prevent theentrance of water vapor into the N gas line.

The process that is disclosed herein is believed to be the first toemploy silicon nitride as a dielectric for capacitors. A hightemperature capacitor is fabricated by the 6 deposition of thin films ofsilicon nitride and of molybdenum by the disclosed thermochemicaldecomposition of chemical compounds from the vapor phase at hotsubstrate surfaces.

The process is applicable to not only capacitors but also to otherelectronic component parts that require a dielectric capable offunctioning at 500 C. and above and that are used in electronic circuitsof guided missiles, satellites, space vehicles and the like.

The chemical reactions that occur in the disclosed process of thethermo-chemical decomposition of metal compounds from their vapor phasesinclude the deposition of silicon nitride dielectric as .a film fromsilicon tetrabrornide vapor that is reduced by hydrogen in the presenceof nitrogen gas at the surface of a molybdenum disc, the temperature ofwhich disc is about between 930 C. and 1030 C. at the surface where thesilicon nitride is deposited, the silicon nitride reaction may beregarded as being The gas mixture flow rate may be illustratively about300 ccs. per minute H with about 1100 ccs. per minute N Theoreticallyother silicon halides should function interchangeably with silicontetrabromide.

The deposition of molybdenum on top of the silicon nitride film may beregarded as being by the thermochemical reduction by hydrogen ofmolybdenum pentachloride vapor at a surface the temperature of which isabout 810 C. The vaporization of molybdenum pentachloride isaccomplished at 194 C. or above, depending on the desired rate ofdeposit-ion. The MoCl vapor so produced is carried by H flowing at anillustrative rate of one liter per minute and flowed against the siliconnitride coat on the substrate maintained at a temperature of between 800and 850 C. where a molybdenum film is deposited according to thereaction:

The silicon nitride on molybdenum type of capacitor that is disclosedherein possesses physical characteristics which establish itssuperiority of performance over previously available capacitors. Acapacitor that embodies the present invention when placed within amufiie furnace and heated stepwise from 25 C. to above 600 C. providescapacity and dissipation factors that are as follows:

Resistance, Capacity, Dissipation RC Product Temp, C. Megohms mmf.Factor Megohms,

microfarads Dielectric Strength:

1,000 Volts/Mil at 25 o.

060 Volts/Mil at 500 0.

From the values that appear in the above chart it will be noted that thecapacity and the dissipation factors increase from a capacity of 2714mmf. at 1000 cycles per second and a dissipation below 1X10- at 25 C. toa capacity of 2763 mrnf. at 1000 cycles per second and a dissipation of33x10" at 600 C. The high temperature characteristics of a capacitor inaccordance with the invention are believed to be unique.

It is within the scope of this invention that multiple alternated filmsof silicon nitride and molybdenum may be applied to a substrate.

In the miniaturization of electronic systems optimum space utilizationmay be accomplished by connecting two or more electronic components withwire that in and of itself is the capacitor that is required in thatcircuit. It is within the concept of this invention that an elecrricallyconductive wire is coated with a dielectric film over which is bonded afilm of another conductor with or without encapsulation. A wire ofmolybdenum coated with a film of Si N over which is a conductive filmsuch as the molybdenum film disclosed hereon then constitutes thecapacitor plates with the silicon nitride film providing the dielectrictherebetween. At opposite ends of the wire one capacitor plateconnection is the wire itself and the other capacitor plate connectionis soldered to the Mo film, as the wire 61 is soldered to the Mo film 44in FIG. 4. This concept is of particular value in missiles, rockets,satellites and the like because of the space-weight conservation factor.It will be apparent that the metals and the compounds disclosed hereinmay be replaced by other similar materials without departing from thisinvention.

Although the preferred embodiment of the invention, the use ofmolybdenum as the metal substrate on which the film of silicon nitrideis deposited, has been described it should be understood that othermetals such as platinum, stainless steel, gold, nickel, and nickelcopper alloys such as Monel metal are also suitable for use as asubstrate forming one layer of the capacitor. In the deposition of aconducting layer on the layer of silicon nitride dielectric, whilemolybdenum is the preferred metal because of general availability andhigh temperature characteristics, other metal coatings can be used. Forexample, platinum may be plated onto the silicon nitride dielectricsurface utilizing an arrangement in accordance with FIG. 2 of thedrawings in which the platinum is plated out onto the heated surface ofthe dielectric coated substrate by mixing platinum carbonyl chloridewith nitrogen as a carrier to decompose on the surface of the substrateas a metallic platinum.

Similarly, nickel can be plated by the decomposition of nickel carbonyl.Gold preferably would be applied by the well known cathodic sputteringprocess or by evaporation of molten gold in a vacuum. The metal chromiumis also satisfactory as a plate material and can be plated bydecomposition of chromium hexa carbonyl.

'It is noted that the various carbonyl compounds listed above willdecompose on the heated surface of the substrate in the region of from100 to 300 C. to leave a metallic plated film. Since the carbonylcompounds are easily volatilized they may be introduced as a vapor intothe apparatus disclosed in FIG. 2 and the plating process carried outuntil the plating has built up to a desired thickness, for example; /2to 1 mil thick. Where platinum is used as a substrate and the metalplating on the silicon nitride coating is also platinum it is notnecessary to encapsulate a capacitor so constructedwbecause of the highresistance of platinum to oxidation. Where substrates of metals otherthan molybdenum are employed a suitable high temperature solder such asgold or gold alloys should be employed for soldering the leads to thecondenser plates it being necessary however that the solder employedshould have a melting point considerably above 625 C.

While the substrate has herein been primarily disclosed as being a flatdisc it is conceivable the substrate can be in the form of a metal rodor tube of a suitable high temperature resistant metal of the type aboveoutlined so that the cylindrical capacitor will be in form.

Further, it is noted that the process of depositing a thin protectivefilm of silicon nitride described above for encapsulating a capacitorcan be employed as a protective coating on other apparatus made of metalwherein it is desired to protect the metal against oxidation when placedin environments where the temperatures may rise to the order of 500 to600 C.

Having now described our invention we claim:

1. A capacitor comprising a metal substrate, a thin film of siliconnitride dielectric covering said substrate and a metallic conductorplate on the exposed surface of the dielectric.

2. An electrical capacitor comprising a first metal plate, a metalconducting film separated firom said plate and a plate of siliconnitride dielectricmaterial positioned between the said first metal plateand said metal conducting film, the dielectric plate being nonporous andbonded to both said plate and said conducting layer. 7

3. The capacitor that is stable at temperatures approaching 600 C.,-andcomprising a substrate of molybdenum, a first electrically conductinglead wire with one end connected to the molybdenum substnatqladielectric film of silicon nitride bonded to the surface of thesubstrate, a film of molybdenum bonded to the silicon nitride dielectricfilm, and a second electrically conducting lead wire with one endconnected to the molybdenum film.

4. The capacitor comprising a substrate capacitor first plate, a film ofsilicon nit-ride bonded to the substrate capacitor first plate, a filmof molybdenum bonded to the film of silicon nitride, a first lead wirewith an end gold soldered to the substrate capacitor first plateadjacent an edge thereof, and a second lead wire with an end goldsoldered to adjacent the edge of the film of molybdenum spaced by thesilicon nitride film firom the molybdenum substrate.

5. The capacitor comprising a capacitor first plate of molybdenumserving as a substrate, a first wire with one end gold soldered to themolybdenum substrate capacitor first plate adjacent the edge thereof, afilm of silicon nitride on the molybdenum substrate as a dielectric withrespect thereto, a second capacitor plate film of molybdenum on thedielectric film of silicon nitride, and a second wire with one end goldsoldered to the molybdenum film capacitor second plate and with its goldsoldered junction.

6. The capacitor defined in the above claim 5 encapsulated within asealing film of silicon nitride References Cited in the file of thispatent UNITED STATES PATENTS Erlwein Mar. 24, 1891

1. A CAPACITOR COMPRISING A METAL SUBSTRATE, A THIN FILM OF SILICONNITRIDE DIELECTRIC COVERING SAID SUBSTRATE AND A METALLIC CONDUCTORPLATE ON THE EXPOSED SURFACE OF THE DIELECTRIC.